$line .= $fh_iterator while $line =~ m{\\$};

##</code><code>##

$line .= $fh->getline while $line =~ m{\\$};

##</code><code>##

Use of uninitialized value $line in pattern match (m//) at parser3.pl line 17, <GEN0> line 5.

##</code><code>##

Use of uninitialized value $line in pattern match (m//) at parser3.pl line 17, <GEN0> line 5.

##</code><code>##

#/usr/bin/perl
use strict;
use warnings;

use IO::File;

use 5.010;

my $filename = shift @ARGV;

my $fh = IO::File->new($filename, 'r');

sub fh_iterator {
    my $fh = shift;

    my $line = $fh->getline;
       $line .= fh_iterator($fh) while $line =~ m{\\$};
}

while (my $line = fh_iterator $fh ) {
    print $line;
}
__END___
test.file
foo \
bar \
baz
single line